Generally forklift trucks (hereinafter referred to simply as "forklift") are statutorily required to have all their tires checked for air pressure prior to the day's operation and have the tires filled with air to the specified level. To have the tires filled with air every morning, in most work shops, the forklifts must be brought to the filling station every morning. If tires are deflated excessively, they have to be removed from the forklift, brought to the filling station, filled with air, brought back to the forklift, and remounted on the forklift. These processes are complicated and time-consuming. The tire filling processes may be simplified when an air compressor is prepared, and compressed air produced by this compressor is led to the packing sites of the forklifts by pipes and hoses for ready use for tire filling. However, since this method requires a large sum of capital to be invested, only large scale forklift workshops where many forklifts are employed can adopt it.
If each forklift is provided with a compressed air producing device and storing device, tire air control can be most conveniently maintained. At present, some forklifts are equipped with an air compressor driven from the engine by belts, but since such an air compressor is quite expensive, comparatively few workshops can afford it.